Grid controlled magnetron apparatus for frequency controllable systems



APIil 3, 195i. P. H. PETERS, JR 2,547,659

GRID coNTReLLED MAGNETRON APPARATUS FOR FREQUENCY CONTROLLABLE SYSTEMS Filed May 7, 1947 GRID CA THODE I/LTA 6E AIVODE CAYHODE VOL TA 6E REA CTA NCE SE C 770Al RECTAA/CE `S'ECT/O/V F: Z

CONTROL VOLTH GE Figi ll'" v 23 27 llll ff Il His Att orrwey.

:trol voltage.

attained by the provision of a grid control mem- -atented pApr. 3, 19,51

GRID CONTROLLED MAGNETRON APPARA- TUS FOR FREQUENCY CONTROLLABLE SYSTEMS Philip H. Peters, Jr., Schenectady, N. Y., assigner to General Electric Company, a corporation of New York Application May 7, 1947ser`ia1No. 746,574

Patent 2,528,241, dated October 31, 1950, by Philip I H. Peters, Jr., and John P. Blewett entitled Frequency Controllable Magnetron, and like the system of the latter application, it will be found to be particularly useful in apparatus of the type described and claimed in my U, S. Patent 2,490,- 007, dated November 29, 1949, and entitled Frequency Controllable Magnetron Systems. Both .of these patents are assigned to the same assignee as the present application.

The general object of the present invention may be considered to be the improvement of systems `of the type of the aforesaid patents in respect to 6 Claims'. (Cl. S15-39).'

the certain operating characteristics thereof, for

example, by providing an improved apparatus of relation between frequency deviation and the control voltages applied to the system to effect such deviation, that is, by providing a more linear relation between frequency deviation and the con- Generally speaking, this object is ber to control the variable reactance characteristic of the space charge between the cathode and anode electrodes of the reactance section of the magnetron device described in the aforementioned Peters and Blewett patent.

The features of the invention desired to be protected are set forth in the appended claims. The

invention itself together with further objects and advantages thereof will best be understood by reference to the following specication and the accompanying drawing in which Figure 1 represents graphically a Vcharacteristic curve cf one operating characteristic of the system of the frequency deviation and the control voltageof the present invention; Figure 4 represents a plan View of a practical magnetron type discharge device embodying the invention; Figure 5 represents a side view of Figure 4; while Figures 6 and '7 represent alternative grid-cathode constructions employable in the devices of Figures 2, 4 and 5.

Broadly speaking, the aforesaid Peters and Blewett patent describes a system in which frequency control of a magnetron circuit may be obtained by the use ofhwhat may be termed a magnetron reactance tube, that is, a tube having a variable electronic reactance employable to con trol the frequency of the system. To that end, the tube incorporates in addition to an oscillator section comprising a set of the usual electrodes energized by a rotating space charge, a reactance section comprising an additional set of electrodes spaced about a second rotating space charge which can be made to behave as a variable electronic reactance. In this respect, the respective reactance andpscillation sections may be viewed as those corresponding to the reactance and oscillating sections of the system of AFigure 2 which will be described in greater detail hereinafter. By controllably varying the voltage between the anode and cathode electrodes of the reactance section, the reactance thereof may be varied to effect a corresponding control of the frequency of the system. It has been found that the curve indicating the characteristic relation between changes in this anode-cathode voltage and the amount of frequency deviation effected by the corresponding reactance change is often somewhat irregular.,and would be advantageously improved if it could be made more regular, preferably if it could be made to follow a linear relation between frequency deviation and voltage, that is, a relatie-n whereby the frequency deviation is made directly proportional to the amount of voltage change on the control element.

A representative characteristic curve of a device of the kind illustrated in the Peters and Blewett patent is sho-wn in the Figure 1. It will be apparent from this curve that as the control voltage, that is, theanode-cathode voltage of the reactance section is raised, the amount of frequency change thereby effected is subject to a number of irregularities indicated by the sharp points l, 2 and 3 of the curve. The most probable explanation of these irregularities is that they represent certain disturbances in the system caused by the fact that at certain critical anode-r Vcathode voltages the angular velocity of the electron space charge in the reactance section equals or is harmonically related to the angular velocity of the rotating space charge in the oscillating section. By the term harmonic relationship as hereinafter used, I mean broadly any condition wherein the respective angular velocities are substantially equal to each other or to harmonics or subharmonics of each other. When the angular velocity of the space charge of the reactance section is harmonically related to that of the oscillating section, it appears that the reactance section may tend to supply a certain amount of .power of its own to the oscillating system and thereby it causes in some manner the irregularities indicated by the curve in Figure 1'.

As suggested in the aforementioned patents, it is the reactance change in the reactance section which ultimately brings about the desired frequency changes and that reactance change is most probably attributable to changes in the properties, for instance, mean space charge radius and density, of the electron space charge as the anode-cathode voltage of the reactance section is changed. However, the changes in anode-cathode voltage also effect a change in the angular velocity of the rotating Vspace charge and therefore give rise to the possibility that at certain critical anode-cathode voltages in a desired operating range, the angular velocity may be harmonically related to that ofthe oscillating space charge in the oscillating section. The aforementioned irregularities in the curve may then occur within the desired operating range. If, however, the desired change in the space charge properties can be effected without a cor- `responding change in the angular velocity it will obviously become possible to effect the desired space charge control without incurring the risk of matching the angular velocity to that of the oscillating space charge in the oscillating section. For example, if those voltages which determine the respective angular velocities in the reactance and oscillating sections can be made relatively constant, then by proper selection of them the angular velocity of the reactance section space charge may be made to be sufficiently dilerent from that of the oscillating section space charge to preclude the possibility of harmonic relationship at any time. Thereby the possibility of irregularities in the curve is avoided. I have found that such space charge density control without substantial corresponding change -in angular velocity may be effected by the use 'space charge. To the `latter end, the voltage between the grid vand the anode o r lin some cases the cathode-anode voltage, which is the voltage which determines the angular velocity, is maintained substantially constant in order to maintain the angular velocity of the space charge correspondingly constant. A grid controlled system of this type is shown in Figure 2.

Referring now to Figure 2, there are provided a pair of opposing anode blocks 4 and 5 and a third electrically neutral block 6 conductively vattached to the electrically neutral midpoint 'l of the U-shaped end of a parallel transmission line comprising wires 8 and 9 in the manner of the construction described and claimed in United States Patent 2,462,698 by Donald A. Wilbur, assigned to the same assignee as the present application. 'Formed within the three blocks 4, 5

and 6 are two cylindrical magnetron cavities I0 and II provided respectively with thermionic cathodes I2 and I3 as shown. A common magnetic field normal to the plane of the Figure 2 may be supplied by any suitable means indicated schematically by arrow H and a surrounding coil in the manner Vwell known in the art and may be arranged to pass through each of the cavities I0 and II in a direction parallel to the axes of the cathodes. The cavity I I and its associated electrode elements, cathode i3, and anode blocks 4, 5 and 6, will be understood to constitute an oscillating section in the manner similar t0 that described in the Peters and Blewett patent, while the cavity I0 and its associated electrode elements, cathode I2 and anode blocks 4 and 5 will be understood to constitute a reactance section in a manner similar to the reactance section of my above-mentioned patent. In operation, continuous osciLations vmay be generated in the vline comprising the wires 8 and 9 as a `tuned resonant circuit, such oscillations being initiated and maintained by the oscillating section formed about the cavity II. For the purpose of tuning the system any suitable means for varying the resonant characteristics Vof the line comprising the wires 8 and 9 may be provided, for example, the conventional tuning short I4 slideable longitudinally of the line and making contact with its opposite members by means of the spring lingers I5 and I6. Any suitable means for extracting power from the system and supplying the same to external utilization circuits, not shown, may be supplied. Such a circuit is indicated schematically by the resistor I'I connected between appropriate potential points on the transmission line. For the purpose of energizing the oscillating section any suitable means for applying a preferably unidirectional voltage between the cathode I3 and the anode blocks 4, 5 and 6 may be provided, for example, the battery I8. A rotatiing electron space charge of the magnetron type may also be established in the reactance section formed about the cavity I 0 by imposing a similar voltage, as by a battery I9, between the anode blocks 4 and 5, and a grid 2B presently to `be described. Alternatively the voltage may be 'applied between the anode block and cathode I2 where the grid and cathode construction makes that permissible or desirable.

It will be understood by those skilled in the art that when the voltage between the grid '28 and the anodes of the reactance section is maintained substantially constant in the presence of a constant magnetic field, then the angular velocity of the rotating electron space charge established in cavity I 0 will in general be substantially constant. By suitable choice of the potential of the battery I 9, that angular velocity may be l made to be suiiciently different from the corresponding angular velocity of the space charge in cavity Il of the oscillating section to preclude harmonic relationship. In order now to provide for a desired change in the electron space charge density in the reactance section and thereby to tiene may be a source of-frequency modulating signals for continuous wave intelligence transmission and as such, it may constitute a part of the system of frequency modulation described in'my aforementioned Patent 2,490,007, or it may simply comprise a unidirectional potential means for tuning or maintaining constant the frequency of the system, as likewise described in my Patent 2,490,007.

As indicated the grid may comprise a generally cylindrical member extending longitudinally of the cavity I0 and co-extensively therewith; Within the cylindrical member there is provided a longitudinal groove 22 in which the cathode I2 is positioned.

The manner of operationof the system of -Figure 2 may be stated as follows: With respect to the reactance section formed about cavity li), it is known that an electronic tube of the magnetron type can be made to behave as a variable reactance, the value of the reactance depending upon the choice of tube parameters, such as the anodecathode Voltage, grid-cathode voltage, the anode and cathode dimensions and the magnetic field.

Y According to the prevailing view the changes in reactance are due inv some manner to variations in the effective dielectric constant of the interelectrode space occasioned by variation in the properties for instance (mean space charge radius and density), of the electron space charge in the interelectrode spaces. As is known, the space charge properties will be a function of the abovementioned tube parameters. lIf the tube parameters of the reactance section are so adjusted that that section does not by itself, generate self sustained oscillations, that is, if it is subject only to those imposed upon it by the oscillator section, and if the voltage between the grid 20 and the anode blocks Il and 5 be held con-Y stant, then in the absence of the further control effect presently to be described the space charge density will be maintained substantially constant Vas the space charge rotates. If, however, a variable voltage difference be applied between the cathode l2 and the grid 20, then a corresponding .variation in space charge density may be effected. When the grid potential is increased in the positive direction with respect to the cathode, an electron sheath of density generally proportionate to the potential will tend to form over the surface of the grid and the grid will thus serve in a sense as a virtual cathode. When the grid potential is increased in the. negative direction with respect to the cathode the number` of elec- ;trons in the cavity i0 will tend to decrease proportionately. The anode grid potential (of battery I9) will substantially fix the average space .charge radius and the average angular velocity for a fixed magnetic eld. Variations in the cathode-grid potential diiference will vary correspondingly the mean space charge density and thereby the reactance of the section.. However, since the change in the cathode-grid potential has substantially no effect on angular velocity of the space charge there is no risk of encountering the irregularities indicated by the curve of Figure 1. With a representative tube of the construction shown in Figure 4, which is the equivalent of that in Figure 2, I have been able to obtain the representative characteristic curve shown in Figure 3 in which the relation between the frequency deviation and the grid-cathode rvoltage is shown (grid negative with respect to the cathode). It will be observed that the curve is substantially free of any irregularity and moreover, that it is substantially a straight line there- Y by affording a regular linear relation between the formed about the cavity l0 by transposing cathode I3 to that cavity while conversely the reactance section is formed about the cavity Il by similarly transposing cathode `I2 and grid 20 to that cavity.

Referring now to the Figures 4 and 5 of the drawing there is shown in greater detail a practically useful tube embodying the structural aspects of the present invention. The device includes an envelope 23 preferably formed of glass,

; within which is mounted a generally U-shaped conductor 24 which may to advantage be formed of copper tubing. The arms 25 and 26 of the U- shaped tubing extend through the lower end wall of the envelope 23 and are sealed thereto by suitable sealing construction such as the vertical sleeves 2l and 28, which are joined to the envelope andthe arms of the U-shaped conductor to form an hermetic seal. The conductor 24 including its arms v25 and 26 which extend to the exterior of the envelope provide a tunable parallel wire transmission line of the type of the line comprising wires 8 and 9 of Figure 2. Within the envelope 23, a pair of anode-electrode members 29 and 3i) are conductively supported in opposed relation from the arms 25 and 26 respectively of the U-shaped conductor 24. These anode members are spaced at their inner ends thereby forming interaction gaps of the conventional magnetron type about the generally cylindrical cavity 3l: formed in their opposed surfaces by the semi-cylindrical faces 32 and 33 surrounding and co-axial with a cathode 34. The anode members 29 and 3e, the cathode Se and the associated cavity Si will constitute the oscillator section of the magnetron corresponding to the oscillator section of FigureZ formed about the cavity H. To provide a reactance section corresponding to that formed about the cavity l0 of the Figure 2, there may be provided in the construction of Figures 4 and 5 a second pair of anode-electrode members 35 and 3G similarly conductively supported in opposed relation from the arms 25 and 26 of the U-shaped conductor 24. These are likewise spaced at their inner ends and are provided with the semi-cylindrical faces 31 and 38 respectively which denne a generally cylindrical cavity 3Q surrounding and coaxial with the grid-cathode structure. The grid-cathode structure, corresponding to that indicated in the Figure 2, may comprise any` suitable structure such as the generally cylindrical stud 4.0 which extends coaxially with the cavity 39 and coextensively therewith. The stud 40 is provided with a longitudinal groove 4| in its periphery and within this groove the cathode 42 is positioned in generally parallel relation to the axis of the stud.

Any suitable means for supporting the respective cathodes and the stud within their respective cavities may be provided. For example, the cathode 34 is shown as being supported by a pair of lead-in wires 43 and 44 having portions extend-ing through hermetic 4seals to terminals on the exterior of vthe envelope 23. The wire 4A has the exterior terminal 45; that for wire i3 is not shown since it is concealed behind terminal 45 in Figure 4 and behind terminal i9 in Figure 5. The resilient spring member 4G may be intsrposed between the one end of the cathode 34 and its associated supporting lead-in wire i3 in order to provide adequate tension on the cathode and thereby maintaining it in iixed position. The cathode c2 of the reactance section may be Supported by a similar pair of lead-in wires 47 and 48 likewise extending to the exterior of the tube through like hermetic seals to exterior terminals 49 and 58 respectively. Here again a resilient spring-lilac member i may be provided to tension the cathode i2 and is interposed between the one end thereof and the associated Supporting lead-in wire 4'i. As a means for supporting the grid member or stud 58, there may be provided a further lead-in supporting conductor 52 extending through an hermetic seal to terminal 53 or the exterior portion of the tube, the stud is shown as being supported by this lead-in conductor 52 through the medium of the rods 5d, 55, 56 and 5l' which are welded into a rigid framework yand welded to the lead-in conductor 52. Where desired the end shields 5S and 59 aiiixed to the cathode lead-in conductors may be provided for the purpose of intercepting the flow of stray electrons from the active cavities to the envelope wall. The latter expedient is, of course, well known in the art. It will be understood that the oscillator section formed by the two electrodes 29 and 36 may alternatively be constructed in a manner shown in Figure 2, that is in the manner of the tube shown and described in greater detail in the aforementioned Peters and Blewett patent.

t will be understood that the cathode-grid unit comprising the cathode l2 and the stud in have been constructed in order to permit a circuit arrangement wherein the voltage fluctuations of the cathode, while the grid-anode voltage is held constant, will effect the necessary change in space charge density without changing the angular velocity thereof. Therefore, it will be understood that a number of alternative gridcathode constructions may be used to accomplish thc same end. in the Figures 6 and 7 there are shown two possible alternative constructions. That in the Figure 6 comprises a cylindrical stud @Si corresponding to the stud t9 of the Figures 4 and 5 but differing therefrom only in that two diametrically opposed grooves Si and 62 are provided therein in which two wire cathodes 63 and Gli are provided respectively instead of the single cathode i2 of the Figures 4 and 5. These cathodes may be electrically common and supplied by the same lead-in connection as shown in the Figures 4 and 5. AIn the Figure 7 the gridcathode construction is shown as taking the form of a plurality of annular disks 65 concentricaliy surrounding the cathode 66 and rigidly positioned by `welding to rods Bl and 68. These elements may be supported by the same lead-in support structures of the Figures e and 5 and corresponding numerals have therefore been employed. The lead-in supports 59 and l@ correspond to their counterparts in the Figures 4 and 5. It will also be understood that the various cathodes may take any suitable form; preferably they are bare tungsten wires which may be heated to a suitable thermionic emissive temperature although it will `loe understood thatthey maybe coated with any of the numerous emission enhancing materials common in the art. 4 i

It will also be understood that while I have found it preferable to construct the oscillating and reactance sections within a single envelope,l they may nevertheless each be constructed as separate units which may be separately connected to the resonant circuit in which they function- Thus I contemplate, for example, that a separate reactance tube may be constructed by simply omitting the oscillation section comprising anode members 29 and 3l! and permitting their function to be performed in a separate oscillating tube of the type well known in the art.

While I have shown and described particular embodiments of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made without depart: ing from my invention in its broader aspects and I, therefore, aim in the appended claims to cover al1 such changes and modifications as fall within the true spirit .and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. Electrical apparatus of the magnetron type for generating frequency controllable electromag-` netic oscillations comprising, an oscillatory cir-` cuit, anode-c-athode means connected in energy exchanging relationship to said circuit for maintaining a rotating space charge of the magnetron type for generating said oscillations in said circuit, second anode-cathode means connected in impedance controlling relationship to said circuit for maintaining a second rotating space charge of the magnetron type having variable reactance characteristics, an electrostatic control member positioned within said second anode-cathode means, said control member comprising a substantially cylindrical member extending longitu dinally to said chamber and having therein an opening in which the cathode of said anodecathode means is positioned.

2. Electrical apparatus of the magnetron type for generating frequency controllable electromagnetic osciilations comprising, an oscillatory circuit, anode-electrode means connected in energy exchanging relationship to said circuit and de'- fining a space charge chamber adapted to accommodate a rotating space charge of the magnetron type for generating said oscillations in said cir'- cuit, second anode-electrode means connected in impedance controlling relationship to said circuit and defining a second space charge chamber adapted to accommodate a second rotating space charge of the magnetron type having variable reactance characteristics, cathode means for supe plying electrons to said chambers, an electrostatic control member positioned within said second chamber to produce a substantially radial electric field with respect to said anode-electrode means and electrostatically surrounding said cathode for a part of the periphery thereof for controlling the dielectric properties of said space charge.

3. A system for the generation of vfrequency controllable electromagnetic oscillations by means of magnetron apparatus comprising an oscillatory circuit, anode-cathode means connected iii-energy exchanging relationship to said circuit, energizing means for applying an electric potential between said anode-cathode means and energizing means for applying a magnetic eld within said anode-'- cathode region to generate therein a rotating space charge of the magnetron type capable of generating said oscillations in said circuit, second anode-cathode means connected impedance controlling relationship to said circuit, energizing means for applying an electric potential between said second anode-cathode means and a magnetic i'leld within said anode and cathode means and sufficient to generate in said second anode-cathode means a rotating space charge of the magnetron type having variable reactance characteristics but incapable of generating oscillations in said circuit, an electrostatic control member positioned within said second anode-cathode means to produce a substantially r-adial electric eld with respect to the axis of said anode-cathode means and electrostatically surrounding the cathode of said anode-cathode means for a part of the periphery thereof, and means for applying between said control member and the cathode of said second anode-cathodemeans an electrical control potential for controlling the dielectric properties of said second space charge and thereby controlling the frequency of said oscillations.

4. A system for the generation of frequency controllable electromagnetic oscillations by means of magnetron apparatus comprising an oscillatory circuit, anode-cathode means connected in energy exchanging relationship to said circuit, energizing means for applying an electric potential between the anode and cathode of said anode-cathode means and energizing means for applying a magnetic field within said anodecathode region to generate therein a rotating space charge of the magnetron type capable of generating said oscillations in said circuit, second anode-cathode means connected in impedance controlling relationship to said circuit, energizing means for applying an electric potential between said second anode-cathode means and energizing means for applying a magnetic field within said anode and cathode means to generate in said second anode-cathode means a rotating space charge of the magnetron type having variable reactance characteristics but incapable of generating oscillations in said circuit, the electric and magnetic elds applied by said iirst and second mentioned energizing means are so proportioned as to preclude harmonic relationship between the angular velocities of said rotating space charges, an electrostatic control member positioned within said anode-cathode means to produce a substantially radial electric field with respect to the axis of said anode-cathode means and electrostatically surrounding the cathode of said anode-cathode means for a part of the pef riphery thereof and means for applying between said control member and cathode an electrical control potential for controlling the dielectric properties of said second space charge and thereby controlling the frequency of said oscillations.

5. An electrical discharge device of the magnetron type for generating frequency controllable electromagnetic oscillations comprising an oscillatory circuit, anode-electrode means connected in energy exchanging relationship to said circuit and deiining a space charge chamber adapted to accommodate a rotating space charge of the magnetron type 'for generating said oscillations in said circuit, a cathode within said space charge chamber for supplying electrons to said chamber, second anode-electrode means connected in impedance controlling relationship to said circuit and defining a second space charge chamber of generally cylindrical configuration adapted to accommodate a second rotating space charge oi the magnetron type having variablereactance characteristics, a second cathode within said second chamber for supplying electrons thereto, and electrostatic control member surrounding said second cathode for an appreciable part of the periphery thereof and positioned within said second chamber to produce a Substantially radial eld with respect to the axis of said anode-electrode means in electrostatic controlling relationship to said space charge for controlling the dielectric properties thereof.

6. An electrical discharge device of the magnetron type for generating frequency controllable electromagnetic oscillations comprising an oscillatory circuit, anode-electrode means connected in energy exchanging relationship to said circuit and defining a space charge chamber adapted to accommodate a rotating space charge of the magnetron type for generating said oscillations in said circuit, a cathode within said space charge chamber for supplying electrons to said chamber, second anode-electrode means connected in impedance controlling relationship to said circuit and dening a second space charge chamber of generally cylindrical coniiguration adapted to accommodate a second rotating space charge of the magnetron type having variable reactance characteristics, a second cathode within said second chamber for supplying electrons thereto, and an electrostatic control member comprising a plurality of thin plates conductively connected together and positioned substantially perpendicular to the axis of said second cathode.

PHILIP H. PETERS, 5R.

REFERENCES CITED The following references are ,of record in the file of this patent:

UNITED STATES PATENTS FOREIGN PATENTS Country Date Germany Aug. 24, 1938 Number Number 

